Modern high frequency receivers, as used for example in radio, television, telecommunication and automotive radar applications, generally comprise a heterodyne or homodyne receiver for down-converting the received high frequency (HF) signal to an intermediate frequency (IF) by mixing the HF signal with a local oscillator signal generated by a local oscillator (LO). While the frequency of the received HF signal may be in the range of a few kilohertz (kHz) up to hundreds of gigahertz (GHz), the intermediate frequency typically has a fixed value in a range from close to 0 Hz to about 100 megahertz (MHz). A first benefit of the down-conversion is that the signal at the intermediate frequency may be processed more easily, in particular if the frequency of the received signal is higher than approximately 1 GHz. Secondly, a particular frequency component of the received HF signal may be selected by varying the frequency of the local oscillator until the resulting intermediate frequency matches a predetermined frequency. The circuitry for processing the intermediate frequency signal can thus be optimized for the predetermined frequency.
Heterodyne or homodyne receivers are produced on mass scale in the form of integrated circuits. Hundreds or even thousands of identical copies of the same receiver can be produced on a single slice (wafer) of a semiconductor substrate, e.g. using masking techniques. Individual receivers are obtained in a subsequent dicing process by cutting the wafer into dice, each die carrying a single receiver. In a subsequent step, each die is tested for its proper functioning, either by testing the bare die or a device in which the die has been incorporated. Usually a small percentage of dice, typically in the range of a few ppm to a few percent, are found to be faulty and are singled out. The testing procedure generally involves applying high frequency probe signals to the receiver on the die to be tested and measuring the receivers response. However, testing the performance of integrated circuits that operate at high frequencies drastically increases production costs. The biggest impact arises from the use of the high frequency probes, since today's probes are suited for laboratory use only. Furthermore, feeding a high frequency signal to a die is nontrivial as the signal can be very sensitive to the characteristics of the conductors or transmission lines that are employed and to parameters which are difficult to control, such as impedance values of contact pads. Therefore the testing methods employed today are either expensive or not sufficiently reliable. This is particularly problematic in the field of radar applications such as 77 GHz automotive radar circuits, where a failure rate close to zero ppm is required.